It all unfolds before an audience of 2,000-plus journalists, politicians and Hollywood celebrities in a cavernous ballroom at the Washington Hilton hotel.

And it is all about provoking a few laughs.

An Obama one-liner from last year: "In 2008 my slogan was 'Yes We Can.' In 2013 my slogan was 'Control-Alt-Delete'" -- a reference to the disastrous rollout of his landmark health care plan, a reform that was to crown his domestic policy legacy.

In 1993, when Bill Clinton was setting records for low approval ratings after 100 days in office, he had this to say of his beleaguered self: "I don't think I’m doing that bad. After his first 100 days in office, William Henry Harrison had already been dead for 68 days." Harrison was the ninth US president, and died in 1841.

It is all a question of finding just the right tone: be witty and fresh and avoid the jokes bandied about all year, but without overdoing it.

"It's not a science," said Jeff Shesol, a former speechwriter for Clinton who teamed up with comic Mark Katz to craft the 42nd president's correspondents' dinner remarks.

"When a comedian delivers a mean joke, that's one thing. When the president of the United States is standing up in front of a room of 2,000 people -- live on television -- and is making fun of you, it's another thing," Shesol said.

In 2011, Obama poked again and again at the bombastic real estate magnate Donald Trump, who was right there in the audience.

The comic-in-chief made fun of Trump's obsession with doubting whether Obama had been born in the United States. Had he been born abroad, Obama would not be eligible to be president.

- Touchy task -

Since John F. Kennedy's brief dinner remarks in 1962, joking about how an increase in ticket prices to attend the dinner risked harming the city's economy -- ha-ha -- the humor at the roasting has evolved to levels tougher and raunchier.

But it is indeed a delicate high-wire act. In 1998, mired in the Monica Lewinsky scandal that would ultimately lead to his impeachment, how could Clinton avoid saying something -- anything -- about the affair that had the US capital in a full-blown lather?

At the time, Clinton traveled abroad often, and critics said he did so to avoid having to answer the myriad questions he faced about his dalliances with the young White House intern. Shesol and Katz addressed it with utmost subtlety.

"As you know, I have been traveling to other lands quite a lot lately, and I just want to say what a pleasure it is for Hillary and me to be here in your country," Clinton said calmly as he began his speech.

"I've been awestruck by the beauty of your landscape," Clinton said. "Yes, this Washington is a very special place and Hillary and I will never forget our visit here." He earned laughter and applause.

The White House correspondent's dinner is also in sync with the day-to-day news.

In 1981, Ronald Reagan was recovering at the presidential retreat of Camp David in Maryland after the assassination attempt a few weeks earlier at the hotel where the dinner is held.

Reagan gave his speech by telephone, and said: "If I could give you just one little bit of advice, when somebody tells you to get in a car quick, do it."

In 2007, the dinner was held after a horrific mass shooting at Virginia Tech University. Then President George W. Bush said: "In light of this week's tragedy at Virginia Tech, I decided not to be funny. I am not going to try to be the funny guy." He then surrendered the microphone to someone else.

The toughest challenge for the small team tasked with writing this very singular kind of presidential address is perhaps to remember that it seems easy but is anything but that.

"There are a lot of people at the White House who think they are funny and in fact they are funny. But writing a joke for this kind of audience is a different thing," Shesol said.

"Then there is the real danger of the people who think they are funny and aren't at all. And some of them are more important than you are."